It has really bad armor and loses half HP versus a Penal in 1vs1 without PTRS. Make it better or nerf all units, you can choose.
Its not a frontline combat unit if its unupgraded and if its upgraded, it'll obliterate anything, PTRS penals included.
And it was just made better this patch, go read the notes.
You want it to be more durable, you'll have to put it in T3, where soviet "durable" one is and deal with the fact that field is now littered with real AT weaponry and still have it die in 2 shots, like the soviet one.
You fine with that?
You can't have very early game transport and reinforcement unit that is strong against small arms, when it arrives at a time when small arms is all there is on field.
Plus, you still didn't provided any valid reason why should it be any more durable, while ignoring the fact it arrives BEFORE AT guns do and has plenty of space in its time window.